Bluetooth technology is a short-range communications technology for a wide range of devices ranging from mobile phones and computers to medical devices and home entertainment products. As of Bluetooth v4.0 the Bluetooth standard includes Bluetooth Low Energy (BLE), which is built upon the original key features of Bluetooth but also applies to devices that operate with ultra low power wireless connectivity.
Any BLE receiver may be configurable to receive dirty packets (dirty Tx) as specified in the BLE test specification document “Bluetooth Low Energy RF PHY Test Specification” (RF-PHY.TS.4.1.0). Every 50 packets, the carrier frequency offset (CFO), modulation index (h), and symbol timing error (terror) are changed to specific value combinations described in the test specification and shown in table 1 below.
TABLE 1Transmitter parameters for dirty packetsTest runCFOhterror1100 kHz0.45−50 ppm2 19 kHz0.48−50 ppm3 −3 kHz0.46+50 ppm4 1 kHz0.52+50 ppm5 52 kHz0.53+50 ppm6 0 kHz0.54−50 ppm7−56 kHz0.47−50 ppm8 97 kHz0.5−50 ppm9−25 kHz0.45−50 ppm10−100 kHz 0.55+50 ppm
In addition to fixed frequency offset, a defined frequency drift is added to the signal characteristics. This is implemented by adding a sinusoidal low frequency modulation to the signal, with deviation of 50 kHz and a modulation frequency of 625 Hz. The modulating signal is synchronized with the packets so that each alternating packet starts at 0° and 180° of the modulating signal.
That is, a dirty Tx has both an initial carrier frequency offset (CFO) and a carrier frequency drift during transmission.
One of the difficulties is to timely estimate and correct the CFO because the preamble is short (1 octet) and the start of frame delimiter (SFD) should be received in a bit-correct manner. Moreover the drift can be tracked during payload reception.